1. Field of the Invention
The present invention relates to an apparatus and a method of obtaining information related to terahertz waves that are transmitted through or reflected by a sample.
2. Description of the Related Art
A terahertz wave is an electromagnetic wave having an arbitrary frequency band from 0.03 THz to 30 THz. In a terahertz wave band, characteristic absorptions that depend on structures and states of various substances that include biological molecules occur. Utilizing such characteristics, an inspection technology for an analysis and an identification of a substance in a nondestructive manner has been developed. Also, an application to a safe imaging technology as a substitute for X-rays or a high-speed communication technology is expected.
In addition, the characteristics of terahertz waves include a moderate ability to penetrate a sample. For example, a technology for measuring a film thickness of a multilayer film, utilizing this property, is disclosed (Japanese Patent Laid-Open No. 2004-28618). According to Japanese Patent Laid-Open No. 2004-28618, on the basis of a plurality of terahertz wave pulse responses, the film thickness of the multilayer film is determined. These pulse responses are obtained by sampling a time response waveform of the terahertz wave with a probe light. According to this method, the sampling is carried out over all measurement time regions.
In recent years, one application of this property of terahertz waves has been a technology for measuring or inspecting the product quality of tablets in a nondestructive manner. For example, an application to a technology for measuring or inspecting the coating thicknesses of a sugar-coated tablet, a film-coated tablet, and the like is expected. These coating thicknesses affect the disintegration properties or resolvability of the tablets. Also, the tablets are formed by mixing a powdered medicinal agent and an additive. For that reason, an application to a technology for measuring or inspecting the uniformity of the contained amount of the medicinal agent with respect to the additive is hoped for.
These characteristic features directly affect medicinal effects of the tablets. For that reason, a technology for controlling and maintaining the product quality of the tablets is important. At the moment, for this purpose, a portion of the manufactured tablets is extracted, and a destructive inspection is carried out.
According to Japanese Patent Laid-Open No. 2004-28618, a method of shortening a period of time needed to measure the film thickness of the multilayer film is sought.
In addition, in a case where quality control for tablets is performed, instead of the sampling inspection, in future, it may be desired to effect a constant inspection during the manufacturing process, so that all the tablets can be inspected. In order to carry out such a process inspection, a method of measuring and inspecting the samples in a nondestructive manner is desirable, but a method by which this could be achieved has not yet been established. In particular, for the process inspection for medicinal tablets, from a standpoint that a large number of samples are dealt with in a short period of time, a method of monitoring the state of a single table in a still shorter period of time is ideal.